// SmoothScroll for websites v1.2.1
// Licensed under the terms of the MIT license.

// People involved
//  - Balazs Galambosi (maintainer)  
//  - Michael Herf     (Pulse Algorithm)

(function () {

// Scroll Variables (tweakable)
    var defaultOptions = {

        // Scrolling Core
        frameRate: 150, // [Hz]
        animationTime: 500, // [px]
        stepSize: 150, // [px]

        // Pulse (less tweakable)
        // ratio of "tail" to "acceleration"
        pulseAlgorithm: true,
        pulseScale: 6,
        pulseNormalize: 1,

        // Acceleration
        accelerationDelta: 20,  // 20
        accelerationMax: 1,   // 1

        // Keyboard Settings
        keyboardSupport: true,  // option
        arrowScroll: 50,     // [px]

        // Other
        touchpadSupport: true,
        fixedBackground: true,
        excluded: ""
    };

    var options = defaultOptions;


// Other Variables
    var isExcluded = false;
    var isFrame = false;
    var direction = {x: 0, y: 0};
    var initDone = false;
    var root = document.documentElement;
    var activeElement;
    var observer;
    var deltaBuffer = [120, 120, 120];

    var key = {
        left: 37, up: 38, right: 39, down: 40, spacebar: 32,
        pageup: 33, pagedown: 34, end: 35, home: 36
    };


    /***********************************************
     * SETTINGS
     ***********************************************/

    var options = defaultOptions;


    /***********************************************
     * INITIALIZE
     ***********************************************/

    /**
     * Tests if smooth scrolling is allowed. Shuts down everything if not.
     */
    function initTest() {

        var disableKeyboard = false;

        // disable keyboard support if anything above requested it
        if (disableKeyboard) {
            removeEvent("keydown", keydown);
        }

        if (options.keyboardSupport && !disableKeyboard) {
            addEvent("keydown", keydown);
        }
    }

    /**
     * Sets up scrolls array, determines if frames are involved.
     */
    function init() {

        if (!document.body) return;

        var body = document.body;
        var html = document.documentElement;
        var windowHeight = window.innerHeight;
        var scrollHeight = body.scrollHeight;

        // check compat mode for root element
        root = (document.compatMode.indexOf('CSS') >= 0) ? html : body;
        activeElement = body;

        initTest();
        initDone = true;

        // Checks if this script is running in a frame
        if (top != self) {
            isFrame = true;
        }

        /**
         * This fixes a bug where the areas left and right to
         * the content does not trigger the onmousewheel event
         * on some pages. e.g.: html, body { height: 100% }
         */
        else if (scrollHeight > windowHeight &&
            (body.offsetHeight <= windowHeight ||
                html.offsetHeight <= windowHeight)) {

            html.style.height = 'auto';
            //setTimeout(refresh, 10);

            // clearfix
            if (root.offsetHeight <= windowHeight) {
                var underlay = document.createElement("div");
                underlay.style.clear = "both";
                body.appendChild(underlay);
            }
        }

        // disable fixed background
        if (!options.fixedBackground && !isExcluded) {
            body.style.backgroundAttachment = "scroll";
            html.style.backgroundAttachment = "scroll";
        }
    }


    /************************************************
     * SCROLLING
     ************************************************/

    var que = [];
    var pending = false;
    var lastScroll = +new Date;

    /**
     * Pushes scroll actions to the scrolling queue.
     */
    function scrollArray(elem, left, top, delay) {

        delay || (delay = 1000);
        directionCheck(left, top);

        if (options.accelerationMax != 1) {
            var now = +new Date;
            var elapsed = now - lastScroll;
            if (elapsed < options.accelerationDelta) {
                var factor = (1 + (30 / elapsed)) / 2;
                if (factor > 1) {
                    factor = Math.min(factor, options.accelerationMax);
                    left *= factor;
                    top *= factor;
                }
            }
            lastScroll = +new Date;
        }

        // push a scroll command
        que.push({
            x: left,
            y: top,
            lastX: (left < 0) ? 0.99 : -0.99,
            lastY: (top < 0) ? 0.99 : -0.99,
            start: +new Date
        });

        // don't act if there's a pending queue
        if (pending) {
            return;
        }

        var scrollWindow = (elem === document.body);

        var step = function (time) {

            var now = +new Date;
            var scrollX = 0;
            var scrollY = 0;

            for (var i = 0; i < que.length; i++) {

                var item = que[i];
                var elapsed = now - item.start;
                var finished = (elapsed >= options.animationTime);

                // scroll position: [0, 1]
                var position = (finished) ? 1 : elapsed / options.animationTime;

                // easing [optional]
                if (options.pulseAlgorithm) {
                    position = pulse(position);
                }

                // only need the difference
                var x = (item.x * position - item.lastX) >> 0;
                var y = (item.y * position - item.lastY) >> 0;

                // add this to the total scrolling
                scrollX += x;
                scrollY += y;

                // update last values
                item.lastX += x;
                item.lastY += y;

                // delete and step back if it's over
                if (finished) {
                    que.splice(i, 1);
                    i--;
                }
            }

            // scroll left and top
            if (scrollWindow) {
                window.scrollBy(scrollX, scrollY);
            } else {
                if (scrollX) elem.scrollLeft += scrollX;
                if (scrollY) elem.scrollTop += scrollY;
            }

            // clean up if there's nothing left to do
            if (!left && !top) {
                que = [];
            }

            if (que.length) {
                requestFrame(step, elem, (delay / options.frameRate + 1));
            } else {
                pending = false;
            }
        };

        // start a new queue of actions
        requestFrame(step, elem, 0);
        pending = true;
    }


    /***********************************************
     * EVENTS
     ***********************************************/

    /**
     * Mouse wheel handler.
     * @param {Object} event
     */
    function wheel(event) {

        if (!initDone) {
            init();
        }

        var target = event.target;
        var overflowing = overflowingAncestor(target);

        // use default if there's no overflowing
        // element or default action is prevented
        if (!overflowing || event.defaultPrevented ||
            isNodeName(activeElement, "embed") ||
            (isNodeName(target, "embed") && /\.pdf/i.test(target.src))) {
            return true;
        }

        var deltaX = event.wheelDeltaX || 0;
        var deltaY = event.wheelDeltaY || 0;

        // use wheelDelta if deltaX/Y is not available
        if (!deltaX && !deltaY) {
            deltaY = event.wheelDelta || 0;
        }

        // check if it's a touchpad scroll that should be ignored
        if (!options.touchpadSupport && isTouchpad(deltaY)) {
            return true;
        }

        // scale by step size
        // delta is 120 most of the time
        // synaptics seems to send 1 sometimes
        if (Math.abs(deltaX) > 1.2) {
            deltaX *= options.stepSize / 120;
        }
        if (Math.abs(deltaY) > 1.2) {
            deltaY *= options.stepSize / 120;
        }

        scrollArray(overflowing, -deltaX, -deltaY);
        event.preventDefault();
    }

    /**
     * Keydown event handler.
     * @param {Object} event
     */
    function keydown(event) {

        var target = event.target;
        var modifier = event.ctrlKey || event.altKey || event.metaKey ||
            (event.shiftKey && event.keyCode !== key.spacebar);

        // do nothing if user is editing text
        // or using a modifier key (except shift)
        // or in a dropdown
        if (/input|textarea|select|embed/i.test(target.nodeName) ||
            target.isContentEditable ||
            event.defaultPrevented ||
            modifier) {
            return true;
        }
        // spacebar should trigger button press
        if (isNodeName(target, "button") &&
            event.keyCode === key.spacebar) {
            return true;
        }

        var shift, x = 0, y = 0;
        var elem = overflowingAncestor(activeElement);
        var clientHeight = elem.clientHeight;

        if (elem == document.body) {
            clientHeight = window.innerHeight;
        }

        switch (event.keyCode) {
            case key.up:
                y = -options.arrowScroll;
                break;
            case key.down:
                y = options.arrowScroll;
                break;
            case key.spacebar: // (+ shift)
                shift = event.shiftKey ? 1 : -1;
                y = -shift * clientHeight * 0.9;
                break;
            case key.pageup:
                y = -clientHeight * 0.9;
                break;
            case key.pagedown:
                y = clientHeight * 0.9;
                break;
            case key.home:
                y = -elem.scrollTop;
                break;
            case key.end:
                var damt = elem.scrollHeight - elem.scrollTop - clientHeight;
                y = (damt > 0) ? damt + 10 : 0;
                break;
            case key.left:
                x = -options.arrowScroll;
                break;
            case key.right:
                x = options.arrowScroll;
                break;
            default:
                return true; // a key we don't care about
        }

        scrollArray(elem, x, y);
        event.preventDefault();
    }

    /**
     * Mousedown event only for updating activeElement
     */
    function mousedown(event) {
        activeElement = event.target;
    }


    /***********************************************
     * OVERFLOW
     ***********************************************/

    var cache = {}; // cleared out every once in while
    setInterval(function () {
        cache = {};
    }, 10 * 1000);

    var uniqueID = (function () {
        var i = 0;
        return function (el) {
            return el.uniqueID || (el.uniqueID = i++);
        };
    })();

    function setCache(elems, overflowing) {
        for (var i = elems.length; i--;)
            cache[uniqueID(elems[i])] = overflowing;
        return overflowing;
    }

    function overflowingAncestor(el) {
        var elems = [];
        var rootScrollHeight = root.scrollHeight;
        do {
            var cached = cache[uniqueID(el)];
            if (cached) {
                return setCache(elems, cached);
            }
            elems.push(el);
            if (rootScrollHeight === el.scrollHeight) {
                if (!isFrame || root.clientHeight + 10 < rootScrollHeight) {
                    return setCache(elems, document.body); // scrolling root in WebKit
                }
            } else if (el.clientHeight + 10 < el.scrollHeight) {
                overflow = getComputedStyle(el, "").getPropertyValue("overflow-y");
                if (overflow === "scroll" || overflow === "auto") {
                    return setCache(elems, el);
                }
            }
        } while (el = el.parentNode);
    }


    /***********************************************
     * HELPERS
     ***********************************************/

    function addEvent(type, fn, bubble) {
        window.addEventListener(type, fn, (bubble || false));
    }

    function removeEvent(type, fn, bubble) {
        window.removeEventListener(type, fn, (bubble || false));
    }

    function isNodeName(el, tag) {
        return (el.nodeName || "").toLowerCase() === tag.toLowerCase();
    }

    function directionCheck(x, y) {
        x = (x > 0) ? 1 : -1;
        y = (y > 0) ? 1 : -1;
        if (direction.x !== x || direction.y !== y) {
            direction.x = x;
            direction.y = y;
            que = [];
            lastScroll = 0;
        }
    }

    var deltaBufferTimer;

    function isTouchpad(deltaY) {
        if (!deltaY) return;
        deltaY = Math.abs(deltaY)
        deltaBuffer.push(deltaY);
        deltaBuffer.shift();
        clearTimeout(deltaBufferTimer);

        var allEquals = (deltaBuffer[0] == deltaBuffer[1] &&
            deltaBuffer[1] == deltaBuffer[2]);
        var allDivisable = (isDivisible(deltaBuffer[0], 120) &&
            isDivisible(deltaBuffer[1], 120) &&
            isDivisible(deltaBuffer[2], 120));
        return !(allEquals || allDivisable);
    }

    function isDivisible(n, divisor) {
        return (Math.floor(n / divisor) == n / divisor);
    }

    var requestFrame = (function () {
        return window.requestAnimationFrame ||
            window.webkitRequestAnimationFrame ||
            function (callback, element, delay) {
                window.setTimeout(callback, delay || (1000 / 60));
            };
    })();


    /***********************************************
     * PULSE
     ***********************************************/

    /**
     * Viscous fluid with a pulse for part and decay for the rest.
     * - Applies a fixed force over an interval (a damped acceleration), and
     * - Lets the exponential bleed away the velocity over a longer interval
     * - Michael Herf, http://stereopsis.com/stopping/
     */
    function pulse_(x) {
        var val, start, expx;
        // test
        x = x * options.pulseScale;
        if (x < 1) { // acceleartion
            val = x - (1 - Math.exp(-x));
        } else {     // tail
                     // the previous animation ended here:
            start = Math.exp(-1);
            // simple viscous drag
            x -= 1;
            expx = 1 - Math.exp(-x);
            val = start + (expx * (1 - start));
        }
        return val * options.pulseNormalize;
    }

    function pulse(x) {
        if (x >= 1) return 1;
        if (x <= 0) return 0;

        if (options.pulseNormalize == 1) {
            options.pulseNormalize /= pulse_(1);
        }
        return pulse_(x);
    }

    var isChrome = /chrome/i.test(window.navigator.userAgent);
    var isMouseWheelSupported = 'onmousewheel' in document;

    if (isMouseWheelSupported && isChrome) {
        addEvent("mousedown", mousedown);
        addEvent("mousewheel", wheel);
        addEvent("load", init);
    }
    ;

})();